Highly sensitive autocollimator with automatic aiming

Conclusions The designed highly sensitive autocollimator with automatic aiming has a reading stability of ±0.01 and a linearity of ±0.02 within an automatic aiming range of ±6.The system has a response time =0.1 sec and a static aiming error less than 0.005.To realize the maximum measuring accuracy of which the autocollimator is capable, the instrument must be protected from temperature fluctuations and air currents, and placed on a stable fixed base.Translated from Izmeritel'naya Tekhnika, No. 6, pp. 25–26, June, 1973.     

Role of harmful impurities in failure of high-strength steels

Conclusions The high-strength, medium-alloy, martensitic steels subjected to low-temperature tempering are characterized by intragranular adsorption of harmful impurities, which reduces the microductility of intragranular failure. Two types of failure take place in this case: fine-dimpled for the steels with _B 1700 MPa, and quasicleavage with _B 1850 MPa.Fine-dimpled failure is associated with adsorption of harmful impurities at the carbide-matrix and fine nonmetallic inclusion-matrix interfacial boundaries. Quasicleavage is supported by adsorption of phosphorus and sulfur on intragranular interfaces: inherited austenite boundaries, subboundaries, martensite crystal boundaries.A reduction of the content of free phosphorus and sulfur increases the microductility of the fracture surfaces of the high-strength steels and greatly increases the fracture toughness and reliability of the steel in service.Translated from Fiziko-Khimicheskaya Mekhanika Materialov, Vol. 27, No. 5, pp. 89–94, September–October, 1991.     

Standard Gibbs' energies of formation of BaCuO2, Y2Cu2O5 and Y2BaCuO5

The Gibbs' energies of formation of BaCuO₂, Y₂Cu₂O₅ and Y₂BaCuO₅ from component oxides have been measured using solid state galvanic cells incorporating CaF₂ as the solid electrolyte under pure oxygen at a pressure of 1.01×10⁵ Pa BaO + CuO BaCuO₂ G _f,ox ^o (± 0.3) (kJ mol^–1)=–63.4–0.0525T(K) Y₂O₃ + 2CuO Y₂Cu₂O₂ G _f,ox ^o (± 0.3) (kJ mol^–1)=18.47–0.0219T(K) Y₂O₃ + BaO + CuO Y₂BaCuO₅ G _f,ox ^o (± 0.7) (kJ mol^–1)=–72.5–0.0793T(K) Because the superconducting compound YBa₂Cu₃O_7– coexists with any two of the phases CuO, BaCuO₂ and Y₂BaCuO₅, the data on BaCuO₂ and Y₂BaCuO₅ obtained in this study provide the basis for the evaluation of the Gibbs' energy of formation of the 1-2-3 compound at high temperatures.     

Variation of the optical energy gap with γ-radiation and thickness in Bi-thin films

The effect of -radiation and thickness on the optical energy gap of Bi-thin films has been investigated by measuring their optical absorbance. The measurements were carried out on thermally evaporated films having thicknesses in the range 5–20 nm. Different -radiation doses were used ranging from 0–300 Mrad. The optical energy gap as well as the absorption coefficient were found to be -dose dependent.     

Static and Dynamic Tearing of Thin Steel Sheets

This paper presents the energy analysis of static mode III fracture of thin steel sheets. For dynamic tearing studies we used the Charpy test apparatus. Static tearing tests performed on three types of steel sheets indicate that the linear relationship of Mai and Cotterell is valid for specimens with a leg width W up to 30 mm. In the given range, the specific work of fracture _e is determined according to the Mai–Cotterell model. The _e kinetics is studied as a function of the sheet thickness B, radius of curvature , and loading rate V. The modified model includes a linear dependence of versus W. Moreover, we show that variation of the loading rate V from 1 to 300 mm/min has no effect on the specific work of fracture _e. A slight decrease in the dynamic fracture toughness J_0,d has been found.     

Effect of shields on radiative heat transfer within the penetration zone

A procedure is proposed for calculating the effect of thin floating shields and of cooled cylindrical shields on radiative heat transfer within the penetration zone.Translated from Izhenerno-Fizicheskii Zhurmal, Vol. 23, No. 4, pp. 627–634, October, 1972.     

Structure parameters governing fracture toughness of engineering materials

Conclusions 1. Of the two concepts of brittle fracture of engineering materials based on the decohesion and coalescence fracture mechanisms, respectively, the first reflects the threshold fracture toughness for materials of perfect structure, the second — the minimal fracture toughness of the material of a real structure. Since the coalescence fracture mechanism is observed with most engineering materials and requires higher fracture energy and the decohesion mechanism is a part of the coalescence mechanism, it is necessary to investigate both of them in order to study the nature of the fracture process and to optimize the material structure. 2. The model parameters on which the coalescence fracture mechanism is based, namely, characteristic distance X_c and microcleavage stress _f ^* , are directly related to the material minimal fracture toughness and are defined by the weakest elements of its microstructure. 3. Rigorous physical interpretation of the characteristic distance and microcleavage stress requires statistical (dimensional and orientation) consideration, yet modeling of the fracture process in mean values of the above parameters seems to be useful. 4. Fracture toughness dependences on the temperature and loading rate both for a number of ceramic materials and for steels in the brittle-to-ductile transition region have much in common. For this reason, it is possible to use some fracture models, and, in particular, the K_µ-model, to analyze fracture of ceramic materials and to optimize their structure. 5. The main ways of enhancing fracture toughness of engineering materials are associated not only with the plasticization of the latter but also with the creation of such structures that would contribute to an increase of their minimal fracture toughness values. This can be achieved by increasing each of the two fundamental parameters of the material fracture micromechanism: characteristic distance and cleavage stress.Institute of Strength Problems, Ukraine Academy of Sciences, Kiev. Université de Metz. Published in Fiziko-Khimicheskaya Mekhanika Materialov, Vol. 29, No. 3, pp. 113–123, May–June, 1993.     

The rate-controlling mechanism(s) during plastic deformation of polycrystalline NaCl at 0.28–0.75 TM

The plastic deformation kinetics of polycrystalline 99.9% NaCl were determined in compression at 23–532°C (0.28–0.75TM) and a strain rate = 8.3 × 10–4 s–1. The rate-controlling mechanism at 0.28–0.65 TM (/ < 3 × 10–4) was deduced to be the intersection of forest dislocations with a Helmholtz free energy F* = 113 kJ/mol (0.16 b3). The forest dislocation obstacles become ineffective at 0.65TM. The kinetics at 0.75TM (/ > 3 × 10–4) were in accord with the Weertman-Dorn creep equation. At T > 0.5 TM the decrease in strain hardening with strain and temperature was attributed to cross slip, leading to a brittle-to-ductile transition at 0.5 TM. Dislocation climb was deduced to become more important at higher temperatures. The stress-strain curves were described reasonably well by the Bergström-Roberts dislocation multiplication model.     

Influence of threshold parameters on cleavage fracture predictions using the Weibull stress model

This study explores applications of three-parameter Weibull stress models to predict cleavage fracture behavior in ferritic structural steels tested in the transition region. The work emphasizes the role of the threshold parameters (_th and _{w – min}) in cleavage fracture predictions of a surface crack specimen loaded predominantly in tension for an A515-70 pressure vessel steel. A recently proposed procedure based upon a toughness scaling methodology using a modified Weibull stress (^* _w) extends the calibration scheme for the Weibull modulus, m, to include the threshold parameters. The methodology is applied to calibrate the Weibull stress parameter for the tested material and then to predict the toughness distribution for the surface crack specimen. While the functional relationship between ^* _w and m suggests a strong effect of the threshold stress, _th, on the calibrated m-parameter, the results show a remarkably weak dependence of fracture predictions on _th as does the dependence of fracture predictions on _w–min for this specimen.     

Strengthening in a DS casting Ni3Al base alloy IC6

A unidirectionally solidified casting base alloy IC6, with the chemical composition (at.%) 16.3–17.6% Al, 8.0–8.3% Mo, 0.16–0.78% B, Ni balance has been developed for advanced gas turbine blades and vanes. The experimental results show that this alloy has high yield strengths from room temperature to 1100°C, excellent creep resistance at temperatures up to 1100°C. The microstructural observations and analysis indicate that the superior mechanical properties of this alloy may be attributed to solid solution hardening by the large molybdenum addition, second phase strengthening by phase and other minor phases that precipitate in various temperature ranges, the formation of a raft structure during creep, and to the existence of high density misfit dislocation networks at / interface areas due to a high value of / misfit.Abbreviations BSE back scattered electron - DS unidirectionally solidified - EDS energy dispersive spectroscopy     

Microstructural development in cast alloys based on the β-NiAl–β′-Ni2AlTi–γ′-Ni3Al–α-Cr system

An investigation of microstructural development in three arc-cast Ni–Al–Cr–Ti multiphase alloys derived from the B2 type -NiAl phase is presented. Detailed microstructural characterization of Ni–25 at % Al–20 at % Cr–15 at % Ti, Ni–26 at % Al–21 at % Cr–11 at % Ti and Ni–25 at % Al–24 at % Cr–15 at % Ti materials by transmission electron microscopy (TEM), is described. Microstructural development is examined in both the as-cast condition and after 140 h homogenization treatments at both 850 and 1100 °C. The formation of a eutectic between an L21-type phase (Heusler phase, with a nominal composition of Ni2AlTi) and elemental -Cr is examined. The precipitation of within () and vice versa, in both the inter- and intradendritic regions, is considered. The formation of L12-type (nominally Ni3Al) precipitates within the and -phases is discussed, as is the transformation of to two-phase / during ageing. © 1998 Chapman & Hall     

Growth and Properties of V-Doped CdxHg1 – xTe Crystals

Cd _x Hg_{1 – x} TeV (x= 0.9–0.95) crystals were prepared by two versions of Bridgman growth, and their optical homogeneity and transport properties were studied. The electrical resistivity of the crystals was 10⁴to 10⁸ m. From the temperature dependences of the Hall coefficient, the activation energy of the vanadium level in Cd _x Hg_{1 – x} TeV was determined to be 0.73–0.82 eV.     

Scaling and dynamics of an interfacial crack front

We report on in situ observations with a high speed CCD camera of an in-plane crack propagating through a transparent heterogeneous Plexiglas block. The toughness is controlled artificially and fluctuates spatially as a random noise. A stable crack in mode I was monitored by loading the system by an imposed displacement. We show that the movement of the fracture front is controlled by local instabilities triggered by the depinning of asperities even for very slow loading. Development of crack roughness is described in terms of a Family-Vicsek scaling with a roughness exponent =0.60 and a dynamical exponent =1.2. We also study the system numerically using a Green function technique. We find =0.6 and =1.5 in contrast to earlier numerical studies that reported a much smaller roughness exponent 1/3. We discuss this discrepancy.     

Radiation of internal waves during vertical motion of a body through a nonuniform liquid

Energy losses to radiation of internal waves during the vertical motion of a point dipole in two-dimensional and three-dimensional cases are computed.Notation _o(z), p_o(z) density and pressure of the ground state - z vertical coordinate - v, p, perturbed velocity, pressure, and density - H(d 1n _o/dz)^–1 characteristic length scale for stratification - N=(gH^–1–g²c _o ^–2 )^1/2 Weisel-Brent frequency - g acceleration of gravity - c_o speed of sound - vertical component of the perturbed velocity - V vector operator - k wave vector - frequency - d vector surface element - W magnitude of the energy losses - (t), (r) (x)(y)(z) Dirac functions - v_o velocity of motion of the source of perturbations - d dipole moment of the doublet - _o,l length dimension parameters - _o intensity of the source Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 39, No. 4, pp. 619–623, October, 1980.     

Influence of calcination and sintering temperatures on the structure of (Pb1 − xBax )ZrO3

(Pb1–xBax)ZrO3 powders are synthesized below 800 °C for x 0.25 using a semi-wet route involving solid-state thermochemical reaction in a mixture of ZrO2 and (Pb1–xBax)CO3. The (Pb1–xBax)CO3 precursors were obtained by a forced coprecipitation technique. These powders can be sintered to achieve nearly 99% of the theoretical density at 1050 °C, which is 200 to 300 °C lower than that employed for the solid state route. The structure of as-calcined powder is orthorhombic for x 0.10 and rhombohedral for 0.25 > x 0.35, whereas the two phases coexist for 0.15 x 0.25. The structure of sintered material is orthorhombic for 0 x 0.10, rhombohedral for 0.20 x 0.30, and cubic for x 0.35, whereas orthorhombic and rhombohedral phases coexist at x = 0.15. The difference in the structure of the as-calcined and sintered powders is discussed in terms of particle size effect and chemical homogenisation of Ba2+ in the PBZ matrix.     

Long-lived induced Raman bands, appearance and ? 4 cm?1 shift of “500” band as a result of pulsed IR(520–640 cm?1) laser irradiation on YBaCuO single crystals

Single crystal YBa₂Cu₃O_6.4 ¯Ec irradiation by CO₂-Ar laser caused (1) a shift of the 500 Raman band (480–490 cm^–1), which means the appearance of the superconducting phase in the focus spot (proved by preliminary results of the inductive method); (2) the increase in intensity of many weakly lived Raman bands that usually look like pedestals of the 500 band (they were observed before as strictly reversible Ar⁺ laser photoinduced bands). The additional (10 components) structure was developed in the region 400–600 cm^–1 on the Raman spectra by comparison of spectra for samples before and after irradiation. By reconstruction of such spectra we analyzed the composition of the sample, which was assumed to be a mixture of microregions with different oxygen content.     

Phase transformations in plasma source ion nitrided austenitic stainless steel at low temperature

Plasma source ion nitriding has emerged as a low-temperature, low-pressure nitriding approach for low-energy implanting nitrogen ions and then diffusing them into steel and other alloys. In this work, 1Cr18Ni9Ti (18–8 type) austenitic stainless steel was treated at a process temperature from 280 to 480 °C under an average nitrogen implantation dose rate (nitrogen ion current density) of 0.44–0.63 mA cm^–2 during a nitriding period of 4 h. The nitrided surfaces of the stainless steel were characterized using Auger electron spectroscopy, electron probe microanalysis, glancing angle X-ray diffraction, and transmission electron microscopy. Below 300 °C, a high nitrogen f.c.c. phase (_N) and an ordered f.c.c. phase () mixed phase and a _N and a nitrogen-induced martensite (_N) mixed phase were obtained respectively under lower and higher nitrogen implantation dose rates. In the range of 300–450 °C a single _N phase was observed under various nitrogen implantation dose rates. Above 450 °C, the decomposition of the _N phase to a CrN phase with a b.c.c. martensite was obtained. Phase states and phase transformations in the plasma source ion nitrided 1Cr18Ni9Ti stainless steel at the low process temperatures are dependent on all the process parameters, including process temperature, nitrogen implantation dose rate, nitrogen ion energy, and processing time, etc.. The process parameters have significant effects on the formation and transformation of the various phases.     

Distinctive features of corrosion cracking of high-strength steels

Experimental data on the corrosion cracking resistance of high-strength steel with a yield limit _0.2 1000 MPa in 3.5 % NaCl solution are presented. It is shown that cracking resistance can be estimated by using the so-called net rated fracture stresses. Corrosion cracking in the surface layers of the metal operating in contact with the medium is explained by the suppression of the processes of plastic deformation.Central Scientific-Research Institute of Structural Materials Prometei, St. Petersburg. Translated from Fiziko-Khimicheskaya Mekhanika Materialov, Vol. 30, No. 1, pp. 42–45, January–February, 1994.     

Synthesis of silicon nitride powder through nitrogen gas atomization

The feasibility of synthesizing silicon nitride powder utilizing reactive atomization processing was analysed. The range of times required for the flight time of particles, the cooling rate of the silicon melt, the reaction time of silicon and nitrogen, and the diffusion of nitrogen through silicon nitride layers were obtained and compared. The results of this study indicated that the production of silicon nitride powder through the reactive atomization process would be limited by diffusion of nitrogen through the nitride (ash) layer, assuming the nitride layer was coherent and the unreacted core model was a valid representation of the liquid silicon-silicon nitride system.Nomenclature k(T) reaction rate constant at temperature, T(s^–1) - k ₀ Arrhenius coefficient - E activation energy (kJ mol^–1) - R gas constant - T temperature (K) - fraction of normalized conversion of -phase in time t - fraction of normalized conversion of -phase in time t - k reaction rate constant for -phase (s^–1) - k reaction rate constant for -phase (s^–1) - k ⁱ intrinsic first-order rate constant for -phase (s^–1) - x conversion fraction of -phase in time t - x conversion fraction of -phase in time t - n reaction order for -phase = 1 - n reaction order for -phase = 0.5 - J diffusion flux (mol m^–2 s^–1) - D diffusivity, or diffusion coefficient (m² s^–1 or cm² s^–1) - dC change in concentration (mol m^–3) - dl change in distance, l (m) - A(_g) gaseous reactant A - B reactant B (may be solid or liquid) - P solid product P - b stoichiometric coefficient of reactant B - p stoichiometric coefficient of product P - t time of reaction passed (s) - time for complete reaction of a particle (s) - X _B conversion fraction - r _c core radius (m) - R _p particle radius (m) - _B molar density of reactant B (mol m^–3) - k _g mass transfer coefficient between fluid and particle (m s^–1) - C _Ag concentration of gaseous reactant A (mol m^–3) - D _e effective diffusion coefficient of gaseous reactant in ash layer (m² s^–1)     

Nucleation and crystal growth of dicalcium phosphate dihydrate on titanium powder

The nucleation and crystal growth of dicalcium phosphate dihydrate (CaHPO₄ · 2H₂O DCPD or brushite) on titanium powder surface has been studied in metastable supersaturated solutions at 37°C and pH=5.50. These experiments were carried out using the constant composition method. In order to determine the effect of substrate size on the kinetics of brushite formation, we used four ranges of titanium particle size (<20 m, 20–45 m, 63–90 m and 90–125 m). The induction period , before the initial crystal growth of DCPD, varied markedly with the relative supersaturation . The initial growth rate R _C of brushite is strongly size-dependent, whereas is relatively constant for the different particle sizes. Plots of Ln R _C versus Ln , for each particle size, gave an apparent order of 3.4±0.2 for the crystallization of brushite on titanium surface. The interfacial energy estimate of 22.9±1.2 mJ m^-2, from the kinetic results, was in the same order of magnitude than that for sparingly soluble salts. Observations by scanning electron microscopy showeed many platelets of DCPD covering the titanium powder surface.